Acidophilous
oak and mixed oak forests are characterised by the dominance of oaks,
usually Quercus robur and Q. petraea, in the tree layer and of
acidophytes of a Middle European[11] or
temperate Eurasian distribution in the lower layers. The shrub and herb
layers are usually well developed, but are relatively species-poor
compared to deciduous forests on more base-rich sites or in climatically
more favourable areas.

These
oak forests extend within the temperate zone of Europe from the
Atlantic coast to western Russia (Map 12). The southern boundary locally
borders on to montane regions of the submeridional zone. The entire
distribution area resembles a fragmented, narrow-angled triangle whose
base extends from northern Portugal (approximately 41° N) along the
Atlantic coast via Ireland to Scotland (approximately 58° N). The tip of
the triangle lies north-east of Kiev (approximately 53° N, 34° E), with
isolated outposts as far east as the Volga at Kasan. The northern
boundary runs through Scotland, southern Scandinavia, Lithuania and
Belarus, and the southern boundary through northern Portugal, northern
Spain, the south of France, northern Italy, Croatia, Bosnia-Herzegovina,
Romania, Ukraine and southern Russia. Southern outliers of these
forests extend into the submeridional zone.

The
soils are characteristically permeable or intermittently moist,
oligotrophic, acidic, often sandy and sometimes shallow or rocky.

As
a result of competition from beech, acidophilous oak forests within the
natural distribution area of beech, particularly in the sub-Atlantic
and Central European floristic provinces, are restricted to
intermittently moist soils or very shallow soils on slopes that are too
dry for the survival of beech seedlings. The naturalness of acidophilous
oak forests is partly a matter of speculation, since in many places
coppicing and coppice with standards have favoured oak in the past.

The
majority of near-natural stands are scattered and relatively small.
Extensive areas occur principally outside the range of beech, i.e. in
western Cantabria and Galicia, south-west France, Ireland and Great
Britain, Poland, Belarus and northern Ukraine.

The
range of the acidophilous mixed oak forests is not as extensive as that
of the summer-green broadleaved forests in general, because there are
additional factors restricting its distribution:

In the montane belt of Central Europe and the submeridional zone, beech forests dominate

In
the north and north-east of its range, competition from coniferous
forests (Formation D) is the limiting factor. On acidic oligotrophic
sites in the east, the deciduous forest formation is less well developed
than coniferous stands in comparison with more base-rich sites (cf.
MONK 1966, quoted from JÄGER 1969: 401). As a result, pure broadleaved
forests are only encountered here on base-rich sites.

In
the east, edaphic and climatic factors (relative lack of precipitation,
warmer summers, more nutrient-rich soils) prevent further development
on acidic soils. For this reason the eastern border of the acidophilous
deciduous forests runs further to the west than the limit of the
broadleaved forest formation in general.

In
the temperate zone, acidophilous mixed oak forests favour the lowland
to colline altitudinal belts. In the submeridional zone on the other
hand, at the southern limit of their range, they are usually associated
with the submontane-montane altitudinal belt. Their characteristic
species combination gradually changes towards the south and
thermophilous sub-Mediterranean oak forests eventually become dominant
(Formation G).

Stand structure and physiognomy (J. Cross)

The
natural structure of these forests is often unclear as the activities
of man and his grazing animals over many centuries still have an
influence today. Near-natural stands consist of five to six layers, i.e.
a first and second tree layer, a shrub layer, a dwarf shrub layer, a
herb layer and a moss layer. In some stands, however, only three layers
may be present.

The
tree layer typically has a 60-90 % canopy cover and reaches a height of
15-25 (35) m. On very shallow, dry soils or in very exposed locations
the stand height may be less than 5 m, while on deep soils it can exceed
30 m. The tree layer is dominated by acid-tolerant oaks (Quercus robur, Q. petraea). Pioneer trees such as birches (Betula pendula, B. pubescens)
play an important role in the regeneration phase on different sites,
particularly in the west, and they persist in the tree layer in mature
stands particularly on intermittently moist sites. In the east, pine and
locally also spruce, can occur admixed with the oak to form the tree
layer. The cover and vitality of the shrub layer depends on the density
of the tree layer as well as the nutrient balance, water supply and
humidity of the site. Members of the Ericaceae or brooms (the latter
particularly in more southern areas) often form a dwarf shrub layer and
in the northern temperate areas of Europe the frequent dominance of
dwarf shrubs lend the forests a boreal character. The herb layer is
usually composed of hemicryptophytes, primarily grasses, woodrushes and
sedges. Geophytes are generally rare, but ferns characteristically play
an important role, particularly in the Atlantic and sub-Atlantic
regions. Pteridium aquilinum can form an additional seasonal layer in
some areas, dense stands of this species displacing almost every other
herb species. The percentage cover and number of species in the moss
layer also vary considerably. In the hyperoceanic west, where epiphytic
communities are a striking feature of the forests, cover can be
particularly high. Cryptogam-rich communities also occur on the
north-west European mainland on the edge of poor, dry forest stands,
where the shrub and herb layer is only poorly developed because of
competition from the tree layer.

Floristic composition (J. Pallas)

European
acidophilous mixed oak forests are characterised by a tree layer
dominated by oaks and an undergrowth in which acidophilous species
prevail. Species of the temperate Middle European floristic region
constitute the greater part of the species composition. In the north and
east of the area, the proportion of Eurasian temperate and Eurasian
boreal taxa increases. In the southern temperate regions of Europe,
numerous sub-Mediterranean species occur in the community, while in the
south-west of the area even some Mediterranean species are present (see Table 12).

Apart from the two Middle European oak species (Quercus robur and Q. petraea) widespread tree species include the frequently intermixed beech (Fagus sylvatica), as well as the Eurasian species Betula pendula and Populus tremula. Within the shrub layer the Eurasian species Sorbus aucuparia, Frangula alnus (almost absent within these forests in the British Isles) and Juniperus communis, as well as elements of the Middle European flora, such as Corylus avellana and to a lesser extent Crataegus monogyna, number among the most frequent species. Frequent and widespread species of the herb layer (see Table 12) include the acidophytes Melampyrum pratense, Pteridium aquilinum, Solidago virgaurea, Agrostis capillaris, Anthoxanthum odoratum, Calluna vulgaris, Deschampsia flexuosa, Molinia caerulea, Holcus mollis, Veronica officinalis, Carex pilulifera, Viola riviniana, Potentilla erecta, Lathyrus linifolius and Danthonia decumbens. The mosses, which are mostly acidophytes, have a circumpolar distribution. Polytrichum formosum, Dicranum scoparium, Hypnum cupressiforme, Leucobryum glaucum, Pleurozium schreberi and Scleropodium purum are
the most frequent species (gaps in the Iberian mapping units may be due
to incomplete records of cryptogams in the vegetation surveys).

Representatives
of the submeridional zone (in Europe these are species of the
sub-Mediterranean sub-region, and to a lesser extent also of the
Pontic-south Siberian floristic region), are primarily to be found
within southern temperate, and especially sub-Mediterranean, mapping
units. Castanea sativa, Sorbus torminalis, Pyrus pyraster, Hieracium sabaudum and Festuca heterophylla are
characteristic. In the northern temperate areas of Europe,
sub-Mediterranean species are almost completely absent from these
forests in the west, while in the east they become more numerous,
presumably due to the more marked summer warmth.

The
most striking floristic divide runs between the sub-Atlantic and the
Central European province. In the Atlantic province, A t l a n t i c
species such as Erica cinerea, Hyacinthoides nonscripta and Ceratocapnos claviculata, as well as Atlantic-sub-Atlantic species, are well represented.

In the sub-Atlantic province many A t l a n t i c - s u b - A t l a n t i c species are still encountered, e.g. Teucrium scorodonia, Hypericum pulchrum, Blechnum spicant, Luzula sylvatica, Galium saxatile, Lonicera periclymenum and Hedera helix.
Lianas seem to develop their greatest vitality (within the acidophilous
oak forests) in the Atlantic areas (Lonicera periclymenum, Hedera helix). In the south Atlantic oak forests, the Mediterranean-Atlantic species Tamus communis and Rubia peregrina also occur.

The great majority of A t l a n t i c species (DT 8.1., 8.1.S in Table 12)
belong to the t h e r m a l - o c e a n i c group of species from the
western side of the continents in the northern hemisphere (cf. JÄGER
1968). It is therefore no surprise that the role of these species
increases continuously within the mapping units in the direction of
their climatic optimum in south-west Eurasia.

Ulex europaeus,
character species of distribution type 8.1. (lusit-atl), is a typical
thermal-Atlantic species. It displays a tendency for a southern Atlantic
distribution, which also characterises other species with similar
requirements. Frequently, species of this group are absent from the
north-west European mainland. Some A t l a n t i c - s u b - A t l a n t
i c species within the acidophilous oak forests (DT 8.2., 8.5.,
8(1).6.) appear in the northern temperate-euoceanic regions of Europe
only in the British Isles and are absent from the European mainland.

Some
A t l a n t i c species occur only in the southern Atlantic
subprovince, sometimes with outposts in the Meridio-Atlantic province
group, e.g. Pyrus cordata, Pseudarrhenatherum longifolium, Daboecia cantabrica, Potentilla montana etc.

These species are grouped together in the newly established Pseudarrhenatherum longifolium distribution type 8.1a. in Table 12 (north
lusit-south atl, cf. MEUSEL et al. in 1965, map 44d). The Iberian
acidophilous oak forests within the 8.1a. area display an increasing
south Atlantic character, in addition to further southern Atlantic
species, endemics, such as Omphalodes nitida, Crepis lampsanoides, Aquilegia vulgaris subsp. dichroa,
occur here. These taxa are also assigned to the DT 8.1a. The greatest
number of Atlantic species occur in the north-west Iberian unit F14.

Another
group of species also inhabits parts of the south Atlantic subprovince,
but in Iberia and to the south it occurs not only in Atlantic areas,
but also in the less oceanic continental interior, where it is
characterised by a preference for the montane altitudinal belt. Unlike
the DT 8.1a. the greater part of the range of these species is in the s u
b m e r i d i o n a l zone. Quercus pyrenaica and Arenaria montana can
be regarded as character-species of this distribution type (JALAS &
SUOMINEN (Ed.) (1976, 1983) map 305 and 688). Their area corresponds to
the western segment of the western sub-Mediterranean DT 5.6. Their
distribution type is therefore newly established as the Quercus pyrenaica type
5.6a.: (west med)-west submed//mo-(south atl). With exclusively
mountain plants, 6.1a. is also possible. Again, some species,
particularly Iberian endemics, only

inhabit parts of this 5.6a.-range.

Additional s u b - M e d i t e r r a n e a n - o c e a n i c species such as Luzula forsteri, Euphorbia amygdaloides, E. dulcis and Polystichum setiferum are likewise concentrated in the southern Atlantic units, but can extend into the central (F17, F21) and the eastern sub-Mediterranean province groups. A frequent distribution type is 5.7.

M e d i t e r r a n e a n species (DTG 1.), such as Quercus suber, Pinus pinaster, Erica arborea, Arbutus unedo, Tamus communis, Rubia peregrina, Ruscus aculeatus, Asphodelus albus, Hypericum androsaemum and Asplenium onopteris within
the mapping units considered here only occur in the south-west within
the south Atlantic areas, in particular in the lowlandcolline units. F14 contains the greatest relative proportion of these species, followed by F7 and F15. The Mediterranean-Atlantic distribution type 1.10. is frequent, i.e. most species are markedly thermal-oceanic.

In
contrast, in the north of the Atlantic province, there are only a few
vascular plant species in the table that thrive as well, or even better,
than they do in the south and in the Meridio-Atlantic province group,
within the acidophilous oak forests. These include Galium saxatile, Blechnum spicant, Luzula sylvatica, Oreopteris limbosperma, Dryopteris aemula, and possibly also Ilex aquifolium and Erica tetralix. Many of these species are montane plants in the eastern part of the sub-Atlantic province.

Most representatives of the Mnium hornum moss
group can be considered as northern temperate-Atlantic-sub-Atlantic. On
particularly poor sites in north-western regions, bryophytes such as Lophocolea heterophylla, Plagiothecium laetum and Aulacomnium androgynum, which grow on raw humus, are characteristic.

The
acidophilous oak woods of western Ireland, and to a lesser extent
western Britain, are particularly noteworthy. There, h y g r i c h y p e
r o c e a n i c, desiccation-sensitive species of cryptogams occur in
an abundance not encountered elsewhere in acidophilous oak forests. In
the Blechno-Quercetum petraeae KELLY (1981), the average number of species is 57.6.

Spermatophytes constitute about 34 % while cryptogams constitute 66 %. Unit F1 represents
an extremely hygric hyperoceanic unit within these oak forests, and is
analogous to the extremely thermal-hyperoceanic unit F14 in Iberia. Ferns, such as Hymenophyllum tunbrigense, H. wilsonii and Dryopteris aemula, wider distributed oceanic bryophytes such as Lepidozia reptans and many extremely Atlantic bryophytes such as Dicranum scottianum are characteristic, but also the liverworts grouped around Adelanthus decipiens are characteristic. These species also occur in the laurel forests of the Macaronesian floristic sub-region (azor-canar-mad).

All
oceanic species groups characteristic of the Atlantic and sub-Atlantic
units are absent from the two eastern provinces of the Middle European
floristic region. The mapping units there are characterised more by an
increase in b o r e a l and E u r a s i a n t e m p e r a t e taxa,
which begin to appear in the north-western temperate areas.
Representatives of this species group include Pinus sylvestris, Picea abies, Vaccinium myrtillus, Luzula pilosa, Maianthemum bifolium, Vaccinium vitis-idaea, Trientalis europaea, Rubus saxatilis, Pyrola rotundifolia, Calamagrostis arundinacea and Orthilia secunda.
Many of these are coniferous forest elements with c o n t i n e n t a l
distribution types (DT 10.3., 10.8., 11.3.). The east European
character also becomes more pronounced with the appearance of a range of
species of the summer-green broadleaved forests, which are absent from
the Atlantic province. The species of the s u b c o n t i n e n t a l Asarum type 8.11., with centres of distribution in the east of the Middle European region, are missing in the Ulex range 8.1.; further, species within the subcontinental 8.13. and 8.14. distribution types should also be grouped here (see Table 12 p. 5). These include Acer platanoides, Euonymus verrucosa, Campanula persicifolia, Carex montana, Peucedanum oreoselinum, Potentilla alba and numerous other species. These species groups play an important role also in the Illyrian F21, located in the eastern part of the central sub-Mediterranean province group, while the Insubrian F17,
also in the central sub-Mediterranean, is characterised by the
coexistence of oceanic and subcontinental species. Amongst the
cryptogams, the species group centred around Dicranum polysetum, differentiates the east European units.

In
addition to the generally distributed sub-Mediterranean species already
mentioned, the Central European and Sarmatian mapping units, especially
the southern Central European F20 and the Illyrian F21,
are distinguished by the presence of characteristic eastern
sub-Mediterranean species with ranges extending into eastern Middle
Europe, e.g. Genista tinctoria, Cytisus nigricans, Genista germanica and others. Nevertheless, a number of representatives of the continental DT 5.9. such as Vincetoxicum hirundinaria or Tanacetum corymbosum can encroach far to the west, particularly into the xerothermic forms of F17 or into the xerothermic sub-Atlantic F18.

The
special phytogeographic role of the s u b m e r i d i o n a l zone is
underlined by the distribution of oak species in the acidophilous oak
forests. Quercus robur and Q. petraea are
the stand-forming species in the northern temperate areas of the
distribution range. In the southern temperate to sub-Mediterranean areas
other oak species occur, such as Q. pyrenaica, Q. canariensis and Q. suber on the Iberian Peninsula or Q. dalechampii, Q. polycarpa, Q. cerris and Q. frainetto in south-east Europe.

…

Mapping units on intermittently moist sites (F3, F9, F22) are characterised by the more frequent occurrence of moisture tolerant species, such as Molinia caerulea, Deschampsia caespitosa, Agrostis stolonifera, Carex nigra and Lysimachia vulgaris. For western units, Myrica gale, Erica tetralix, Narthecium ossifragum and Sphagnum species are characteristic and for Central European-Sarmatian units, Molinia arundinacea and Carex brizoides are typical.

Position in the phytosociological system (syntaxa) (J. Pallas)

Depending on point of view the order of the acidophilous oak forests, Quercetalia roboris Tüxen 1931, is placed in the class Querco-Fagetea or, as originally, in an independent class, the Quercetea robori-petraeae Braun-Blanquet et Tüxen 1943.

The reasons underlying these different views relate to the geographical origin of the authors, since, as can be seen in Table 12, the order Quercetalia contains
a higher proportion of more demanding deciduous forest species in the
southern temperate and submeridional/montane areas of Europe than it
does in the north-west European temperate lowlands.

The Quercetalia roboris Tüxen
1931 includes phytogeographically heterogeneous associations, which are
characterised by the dominance of both acid indicators and
acid-tolerant oaks. The combination of both features is the actual
characteristic of the order.

Compared
to the Atlantic units that contain numerous species characteristic of
extremely oceanic regions (Ireland, north-west Iberia), the sub-Atlantic
units behave as marginal syntaxa without any of their own character
species. On the other hand the boundary between the sub-Atlantic and
Central European province is quite clear, being marked by the loss of
Atlantic-sub-Atlantic species. Nevertheless, compared to the Sarmatian
units with their prominent share of Eurasian or circum boreal coniferous
forest, temperate Eurasian and east European species, as well as their
better trophic conditions, the Central European units behave only as
marginal syntaxa.

In
principle, only the oak forests of the two main centres of diversity
(atl + submed) are positively floristically characterised by the
presence of acidophytes of a European distribution. From a pan-European
perspective, synsystematic problems arise as a result of the
climatically-determined disappearance of Atlantic and
Atlantic-sub-Atlantic species towards the east. The greater species
diversity in the submeridional zone compared to the temperate zone also
has to be considered (cf. MEUSEL & JÄGER 1989).

In Table 12 an attempt has been made to compare as many units of the geographically widespread order Quercetalia roboris as
possible. The following review represents a revision and extension of
the proposals previously published by the author (PALLAS 1996, 2000).
The division is now based exclusively on chorological criteria. Habitat
differences (intermittently moist units) are classified into sub-units
according to geographic criteria.

The
special position of the extremely oceanic oak forests should be clearly
indicated by establishing separate alliances. These units represent
centres of diversity in their own right. The Hymenophyllo-Quercion encompasses the Irish hygric hyperoceanic oak forests and the Quercion robori-pyrenaicae constitutes
the thermal hyperoceanic oak forests in north-west Iberia. The
remaining southern temperate acidophilous oak forests of the Atlantic
and sub-Atlantic province belong to the Quercion roboris, and the remaining northern temperate oak forests of the Atlantic and sub-Atlantic province can be grouped in the Molinio-Quercion.
In the same way the oak forests of the Central European and Sarmatian
province can be grouped into a northern temperate alliance, the Vaccinio-Quercion petraeae and a southern temperate alliance, the Agrostio-Quercion. The central and eastern sub-Mediterranean acidophilous oak forests belong to the Castaneo-Quercion.

The alliance Quercion pyrenaicae Rivas Goday ex Rivas-Martínez 1964 [1963] comprises the Quercus pyrenaica woodlands on acid soils, with their main area in the northern Iberian province. The formation subgroup G.4.1., with the units G64toG70, belongs to this alliance. The Quercus canariensis woodlands
of the formation subgroup G.4.4. on silicate rock are also close to
this unit. As a submeridional unit, this alliance can be compared with
the Castaneo-Quercion Soó 1964 (see below).

We
have decided to raise the former suballiances to the rank of alliances.
The different linkages to the vegetation zones and the oceanity of both
alliances should be pointed out: on the one hand temperate southern
Atlantic woodlands, mostly dominated by Q. robur; on the other hand submeridional northern Iberian woodlands, mostly dominated by Q. pyrenaica (see
map). In this way the situation is avoided whereby one alliance covers
two vegetation zones. Further clarification is still required as to
whether the western sub-Mediterranean Quercion pyrenaicae and the central to eastern sub-Mediterranean Castaneo-Quercion might be united within an order of sub-Mediterranean acidophilous oakwoods.

…

Macroclimatic factors (J. Cross)

The
distribution of this formation corresponds with climate type VI and the
more oceanic variant with type V-VI, as well as type V, based on WALTER
et al. 1975 (see Map 2). The large longitudinal and latitudinal range
of this formation indicates that it can tolerate remarkable variations
of climate. In the west, winters are mild with only a few frost days
(average of the coldest month in Great Britain and Ireland is
approximately 3-5 °C), summers are cool (average of the warmest month
approximately 16 °C or less) and the mean annual temperature lies at
approximately 10 °C. Cloud cover and relative humidity are high. This
pattern also applies in the north-west, oceanic areas of mainland
Europe. To the east the climate becomes increasingly more continental:
the precipitation decreases from more than 2000 mm on the west coasts of
Ireland and Britain, to 500-600 mm in eastern Poland and Ukraine and
there is a shift to a summer maximum. The winter temperatures decrease,
with averages of the coldest months ranging from 0 to -2 °C in north
Germany to -12 °C in Russia. In eastern areas continuous frosts and snow
cover can persist for a month or longer. The summers are warmer though
in the east with the averages of the warmest month lying between 16-20
°C and up to 23 °C in Russia. The annual mean temperature, however, is
lower than in the west, mean values being between 6.5 and 9 °C (and 5 °C
in the coldest region in north-east Poland). Southern Sweden has a
somewhat more continental climate than neighbouring areas in northern
Germany. Temperatures increase towards the south in the oceanic areas of
the formation. The highest values occur in south-western France
(average of the warmest month 20-22 °C, and the coldest month 4-6 °C);
on the Iberian Peninsula the summer temperatures are somewhat lower
(approximately 20 °C), but the winter temperatures are higher (6-10 °C).
The precipitation in south-west France shows a pronounced summer
minimum (lowest values around 500 mm). Precipitation increases again to
the west and exceeds 2000 mm locally in the mountains of north-west
Spain. The Insubrian distribution area shows similarities with the
north-west of the Iberian Peninsula with high annual precipitation
(1350-2000 mm), but the temperature of the warmest month, with 25 °C, is
much higher.

Site conditions (J. Cross)

Acidophilous
oak forests occur mainly on acidic, base-deficient soils (podzols,
gley-podzols, base-poor brown earths and ranker). The soils themselves
have developed as a rule from Palaeozoic and Mesozoic siliceous rocks
(sandstone, greywacke, slate, gneiss, other acid metamorphic rocks and
granite) or – in the Central and eastern European lowlands – from
Tertiary and Pleistocene unconsolidated material (moraines, outwash
plains), river sediments or – very locally – drained mires. The soils
are acidic to strongly acidic with a pH of < 4.5 to 5.5, oligotrophic
to oligo-mesotrophic, locally mesotrophic, very permeable, fresh to
dry, locally water-logged. In the uplands the soils can range from
shallow to rocky. In Central and southern Europe, thermophilous forms
occur on warm, sunny, south-facing slopes.

Role in structuring the landscape (J. Cross and U. Bohn)

On
the margins of, and outside the natural range of beech forests, as in
the north-west of the Iberian Peninsula, south-west France, Ireland and
Great Britain, acidophilous oak forests are prominent and characteristic
components of the siliceous uplands, as well as of the nutrient-poor
sandy lowlands (for example the ‘Landes’). In contrast, in western and
Central Europe, i.e. the domain of beech forests, they occur only on
sites inimical to the development of beech. These include highly
oligotrophic and dry sandy soils, water-logged sandy and silt soils of
the lowlands and hills, as well as shallow to rocky, summer-dry to
xerothermic sites within the siliceous uplands. In areas with extensive
stands, such as the Carpathian foothills in Romania, Bohemia,
Piedmont-Insubria and Croatia, they are restricted to the
colline-submontane altitudinal belts below the acidophilous beech
forests. At the margins of, and beyond the range of beech forests in the
central east European lowlands, the acidophilous oak forests occupy
oligotrophic dry to water-logged sandy locations. Here, the tree layer
regularly contains Scots pine and often also spruce. The natural
vegetation complexes include pine forests (on extremely sandy soils,
such as inland dunes), pine-bog forests, wooded raised bogs, birch and
alder carrs (on very wet, peaty sites) as well as oak-hornbeam and
small-leaved lime-pedunculate oak forests on more nutrient-rich sites.

In
addition to the above mentioned azonal forests, the following
vegetation types are also encountered within the formation: mixed
oak-ash forest on base-rich soils (e.g. F19), oak-alder-ash in river
flood plains, oligotrophic mires, raised bogs and (in the euatlantic
area) blanket bogs on sites with poorly drained peats. On naturally
rocky and dry sites, rock heaths, rock scrub and siliceous dry
grasslands occur as adjacent communities.

State of preservation, land use, substitute communities (J. Cross and U. Bohn)

Traditionally, acidophilous oak forests have been used for coppice, but small, near-natural stands

have
persisted in many regions, in Central Europe primarily on extreme
sites. Many of the seminatural coppice stands have been allowed to
develop into high forest, or they have been replaced by plantations of
Scots pine (Pinus sylvestris) or more rapidly growing, exotic conifers, such as Douglas fir (Pseudotsuga menziesii).
Extensive areas of the oligotrophic and poorly productive soils are
unsuitable for agriculture without the regular addition of organic or
mineral fertilisers. In the past, after thinning and forest clearance,
the areas were typically grazed, usually by pigs and sheep. As a
consequence large areas of these forests have been converted to dwarf-
shrub heaths, acidic grasslands, open siliceous grasslands, or –
depending on human activities – to dense stands of bracken. Recently,
many of these heaths have been afforested with conifers, although
grazing still plays an important role in certain areas. Nowadays, in
some areas former grazing practices are being reintroduced for nature
conservation purposes in nature reserves dedicated to preserving the
traditional, cultivated landscapes and their vegetation, often using old
breeds of domesticated animals Arable land is concentrated on dry areas
of the lowland units, where arable crops such as barley, oats, rye,
potatoes and sometimes corn are cultivated.

Nature conservation (J. Cross)

Acidophilous
oak forests remain mostly as small, often derilict stands of old
coppice or high forest and are currently highly endangered in many
areas. The principal threats are from, grazing, clear-felling,
afforestation with conifers and conversion into arable land. Air
pollution and eutrophication from fertiliser drift, especially nitrogen,
represent major problems, particularly in Central and northern Europe,
as they lead to the proliferation of nitrophilous species and brambles.
Overpopulation by game species and (particularly in Great Britain and
Ireland) overgrazing by sheep prevent the regeneration of these forests.
As a consequence, many stands lack a dwarf shrub layer and only possess
a severely degraded herb layer, while the tree layer is often
even-aged. In certain areas, fire also presents a risk, while
recreational use can also present a problem locally. In the wetter parts
of Great Britain and Ireland, the invasion of Rhododendron ponticum,
and locally also beech, pose a serious threat to these forests. Many
countries have established nature reserves, national parks or nature
parks for protecting valuable, semi-natural forest stands and substitute
communities worthy of protection (particularly dwarf shrub heaths,
mat-grass communities, fields of Corynephorus). However, these fall far short of preserving and restoring sufficiently large and representative stands of all forest types.

Classification into subunits (J. Pallas)

In
the overall legend the acidophilous oak forests are subclassified
mainly according to the altitudinal belts they occupy, which are
arranged basically from north to south:

– lowland-colline types (F1-F13)

– colline-submontane types (F14-F22)

– montane-altimontane types (F23-F26).

Within
these belts, the mapping units are, as a rule, arranged from west to
east, from markedly oceanic to subcontinental climates. This is manifest
in the corresponding floristic changes. In addition, ecological
variants are also identified, i.e. hygrophilous (F3, F9, F22), xerothermic (F17 p.p., F18, F20 p.p.) and thermophilous types (F21).

However, in Table 12 and
the following text, the classification is based on on synchorological
criteria, whereby the altitudinal belts are arranged on a regional
basis. The sequence begins with the southern Atlantic units of northern Iberia (F14, F15, F23-F26),
which most clearly demonstrate the thermal-oceanic character of this
area. This is followed by the southern Atlantic mapping units of France (F4-F7), followed by the sub-Atlantic Burgundian unit F16 and the sub-Atlantic Rhenanian unit F18, with the submeridional Piedmontese-Insubrian unit F17 being
placed alongside. The primarily northern temperate units are arranged
from west to east, from the extremely hygric oceanic unit of Ireland (F1) to the Central European and Sarmatian units (F12, F13)
that already show subcontinental traits. The last section of the table
is formed by southern temperate Central European and pre-Carpathian (F20, F22), as well as the submeridional Illyrian (F21), units.

Table 12 is organised according to the vertical struture (tree, shrub, liane, herb and moss layers).

Within
the layers the general character species are listed first. These are
followed by the species characteristic for the Atlantic and sub-Atlantic
units as well as those characteristic for the Central
European/Sarmatian units, consistent with the main dividing line between
the oceanic and subcontinental units. Within each of these groupings
the species are arranged according to their zonal chorological linkages,
i.e. according to their affiliation to the major distribution type
groups. Differential species based on habitat and altitude are grouped
together into their own groups. The literature regarding the individual
mapping units that was studied for compiling Table 12 is cited in the data sheets.